Square Footage Calculator - Area by Shape, Cost & Unit Conversion
Square footage depends on shape. Choose a rectangle, triangle, circle, or trapezoid and the calculator converts the area to square feet, square metres, yards, and cost.
Optional cost uses calculated area in the active unit system.
Change any value and the results, formula, and diagram update immediately. Use the same unit system throughout one estimate.
Square Footage By Shape - Quick Reference
The four common shapes and their area formulas. Use the diagram to verify your shape choice before reading the result.
| Shape | Formula | Example (10 ft dim) |
|---|---|---|
| Rectangle / square | length x width | 10 x 10 = 100 sq ft |
| Triangle | (base x perpendicular height) / 2 | 10 x 10 / 2 = 50 sq ft |
| Circle | pi x radius² | pi x 5² = 78.5 sq ft (10 ft diameter) |
| Trapezoid | (base1 + base2) / 2 x height | (10+6)/2 x 10 = 80 sq ft |
| L-shape / irregular | Sum of sub-rectangles | Break into pieces and add |
For radial shapes (octagon, hexagon, ellipse), break into triangles and rectangles, or look up the specific formula.
Area Unit Conversions
Square footage is one of many area units. The calculator converts between them; reference table:
| From | To | Multiply by |
|---|---|---|
| Square feet (sq ft) | Square metres (m²) | 0.0929 |
| Square feet | Square yards (sq yd) | 0.1111 (divide by 9) |
| Square feet | Acres | 1 / 43,560 |
| Square metres (m²) | Square feet | 10.764 |
| Square yards | Square feet | 9 |
| Acres | Square feet | 43,560 |
| Hectare | Square metres | 10,000 |
| Hectare | Acres | 2.471 |
| Square feet | Cent (India) | 1 / 435.6 |
| Square feet | Gunta (Karnataka) | 1 / 1,089 |
Measuring Real Rooms
- Rectangular rooms: measure length to longest wall, width to perpendicular wall.
- L-shape: divide into two rectangles, measure each, sum.
- Bay window or alcove: calculate as separate rectangle and add.
- Vaulted ceiling: floor area is what gets carpeted; ceiling area is separate (and bigger).
- Stair openings: subtract the stair well from upper floor area (about 50-100 sq ft typical).
- Diagonal walls: calculate as a triangle (base x perpendicular height / 2).
- Curved walls: approximate as circle or polygon segments.
Carpet Area vs Built-Up vs Super Built-Up
Especially relevant for Indian real estate, but matters globally. Property listings often inflate area by using different definitions:
- Carpet area (Indian RERA): usable floor area inside the walls of the unit. Excludes wall thickness, balcony, common areas. The smallest, most honest number.
- Built-up area: carpet area plus wall thickness and balcony. About 10-15% larger than carpet.
- Super built-up area: built-up plus a share of common areas (corridors, lobbies, lifts). Can be 25-40% larger than carpet.
- Gross internal area (GIA) (UK): floor area measured to internal face of perimeter walls. Roughly equivalent to built-up.
- Net internal area (NIA) (UK / commercial): GIA minus common areas, structural columns, lift shafts. Close to carpet area.
- BOMA (US commercial): standard measurement methodology for office and commercial; varies by methodology version.
Common Mistakes
- Using diagonal as edge length - rectangle formula needs perpendicular sides.
- Treating curved or angled sides as straight.
- Forgetting to convert units (sq ft vs sq yd vs m²).
- Using diameter where the formula wants radius.
- Including stair openings, void areas, or unfinished spaces in liveable area.
- Mixing carpet area with super built-up area in property comparisons.
- Using interior floor area for exterior projects (deck, patio) - exterior measurements include overhang.
- Skipping the diagram check - shape mistakes cost the most.
Square Footage Calculator FAQ
How do I calculate the square footage of a room?
For a rectangle: length x width. A 12 x 14 ft room = 168 sq ft. For other shapes, use the formula in the calculator. For L-shapes or odd rooms, divide into rectangles and add.
What is the formula for square footage?
Depends on shape. Rectangle: L x W. Triangle: (base x height) / 2. Circle: pi x radius². Trapezoid: (base1 + base2) / 2 x height. All dimensions must be in the same unit.
How many square feet in 1 square metre?
10.764 sq ft. So a 50 m² room is 538 sq ft. Conversely, 1 sq ft = 0.0929 m².
How do I measure an L-shaped room?
Split it into two rectangles. Measure each rectangle's length and width. Calculate the area of each (L x W). Add the two areas.
What is the difference between sq ft and sq yards?
1 sq yard = 9 sq ft. Carpet and some flooring are sometimes priced per square yard; tile and most materials are per square foot. Divide sq ft by 9 for sq yards.
How do I find the diameter or radius of a circle?
Diameter is the full distance across through the centre. Radius is half the diameter. For a 10 ft diameter pool, radius = 5 ft. Area = pi x 5² = 78.5 sq ft.
How is carpet area different from built-up?
Carpet area is the usable space inside the walls of a room or unit. Built-up adds wall thickness and balcony. Super built-up adds a share of common areas (lobby, corridors). RERA in India requires carpet-area pricing for new construction.
How do I measure a triangular room?
Measure base length and the perpendicular height from base to the opposite point. Area = (base x perpendicular height) / 2. Do not use the slant edge as height.
How accurate are calculated square footage values?
Calculator math is exact for the inputs given. Real-world accuracy depends on how carefully you measure. Use a laser distance meter for accuracy under 1%; tape measures are good to 2-3%.
What is the standard residential room size?
US: master bedroom 200-300 sq ft, regular bedroom 100-150, living room 250-400, kitchen 100-200. India: 1 BHK ~500-700 sq ft total, 2 BHK 900-1,200, 3 BHK 1,200-1,800. UK: similar to India numbers.
Related Construction Calculators
For property and plot area, see the Land Area Calculator. For flooring on the measured area, the Flooring Calculator. For paint coverage, the Paint Calculator. For tile, the Tile Calculator. More tools live on the Construction Calculators hub.
Sources
- ANSI Z765 - Standard for Single-Family Residential Buildings Square Footage Method
- BOMA Floor Measurement Standards for commercial buildings
- RICS Code of Measuring Practice (UK)
- RERA India - carpet area definitions
- ISO 9836 area measurement standards
- NIST Handbook 44 unit conversion tables
This calculator is for planning and ordering conversations. Local code, project drawings, engineered design, and manufacturer instructions control the final work.